This invention relates to cascade type thrust reversers for aircraft turbofan engines and, more particularly, to blocker door assemblies with drag links used in cascade type thrust reversers.
Modern aircraft turbofan engines have a nacelle or shroud surrounding the engine, spaced outwardly from a core engine cowl to define an annular passage or duct for flow of air rearward from the outer portion of a large fan or axial flow compressor. In this type of engine, a large proportion of the total thrust is developed by the reaction to the air driven rearward by the fan. The balance of the thrust results from ejection of the exhaust gas stream from the core engine.
Aircraft using gas turbine engines tend to have high landing speeds, placing great stress on wheel braking systems and requiring very long runways. To reduce this braking requirement and permit use of shorter runways, means are now provided in such engines for reversing a major portion of engine thrust during the landing roll. Many different types of thrust reversers have been designed.
With turbofan engines, it is possible to block and reverse substantially all of the fan flow without excessive stress on the system, since the core flow continues through the engine. In some cases, sufficient reverse flow can be obtained by blocking only a substantial portion of the fan flow. The most common type of thrust reverser used in turbofan engines utilizes sets of cascade vanes in the sidewalls of the engine nacelle with devices for uncovering the cascades to direct the airflow though the cascades, which turn the airflow in a reverse direction.
As turbofan engines become increasingly more complex and efficient, the higher their bypass ratios get. A higher bypass ratio in a turbofan engine leads to better fuel burn because the fan is more efficient at producing thrust than the core engine. As a consequence, the fan gets bigger, and the annular airflow duct between the nacelle and the core engine cowl gets taller. The introduction of a fan drive gear system for turbofan engines has also led to smaller engine cores. Smaller engine cores lead to shorter fan ducts, which are desirable so the heavy components of the engine are not hung out too far in front of the wings of the aircraft. As such, engine sub-systems are required to be packaged within smaller spaces.
The formation of a fan duct thrust reverser typically includes link arms that connect the blocker doors to the inner fixed structure. These link arms are frequently somewhat aerodynamically profiled. However, due to manufacturing costs and maintainability complications a single angle is chosen as a compromise in attempting to reduce the drag effects of the link arms in the fan duct.